Hibernate cfg.xml configuration for sequence generator

问题

Fellow developers, I'm finding it hard to get the sequence generation configured.

I inherited a persistent class with the following id field definition:

@Id
@GeneratedValue(strategy= GenerationType.AUTO)
private Long id;

All of my classes inherit from this class.

The main thing I want: I need to override the strategy of id generation to use HiLo. It has to be in the cfg.xml since it's the only place that I have control over.

This thing looked promising:

<property name="hibernate.id.new_generator_mappings">true</property>

However I couldn't choose the optimize, or the increment size (I want to go HiLo)

<property name="hibernate.id.increment_size">50</property>
<property name="hibernate.id.optimizer">hilo</property>

didn't work, nor

<property name="increment_size">50</property>
<property name="optimizer">hilo</property>

nor

<property name="optimizer">org.hibernate.id.enhanced.HiLoOptimizer</property>

The NoopOptimizer is always chosen.

Any tip will help. Thanks a lot in advance.

回答1:

Let's do some investigation (looking at the Hibernate sources):

The AnnotationBinder defines how AUTO is mapped:

switch ( generatorEnum ) {
  // ...
  case AUTO:
    return useNewGeneratorMappings ? 
      org.hibernate.id.enhanced.SequenceStyleGenerator.class.getName() : "native";
  // ...

If you don't use the NewGeneratorMappings you're stuck with the native implementation. Hibernate will resolve that depending on the database (see this answer to see what that will be for your specific database).

But since you used the NewGeneratorMappings we have to look at the SequenceStyleGenerator:

protected String determineOptimizationStrategy(Properties params, int incrementSize) {

  // ... some stuff to calculate defaultOptimizerStrategy

  // OPT_PARAM = "optimizer"
  return ConfigurationHelper.getString( OPT_PARAM, params, defaultOptimizerStrategy);
}

Assuming the right Properties are passed and you have an "optimizer" property in them then your value should be returned. This value is used to call OptimizerFactory.buildOptimizer (as the first parameter):

 public static Optimizer buildOptimizer(String type, Class returnClass, int incrementSize) {
   final Class<? extends Optimizer> optimizerClass;

   final StandardOptimizerDescriptor standardDescriptor = 
     StandardOptimizerDescriptor.fromExternalName( type ); // HILO("hilo", HiLoOptimizer.class),
   if ( standardDescriptor != null ) {
     optimizerClass = standardDescriptor.getOptimizerClass();
   }
   else {
     try {
       optimizerClass = ReflectHelper.classForName( type );
     }
   catch( Throwable ignore ) {
     LOG.unableToLocateCustomOptimizerClass( type );
     return buildFallbackOptimizer( returnClass, incrementSize );
   }
 }

 try {
   final Constructor ctor = optimizerClass.getConstructor( CTOR_SIG );
   return (Optimizer) ctor.newInstance( returnClass, incrementSize );
 }
 catch( Throwable ignore ) {
   LOG.unableToInstantiateOptimizer( type );
 }

  return buildFallbackOptimizer( returnClass, incrementSize );
}

private static Optimizer buildFallbackOptimizer(Class returnClass, int incrementSize) {
  return new NoopOptimizer( returnClass, incrementSize );
}

So either it finds your value "hilo" (or your "HiLoOptimizer"), instantiates it and returns it or it will log some error message. If you find no error message in your logs I would check whether the properties in the cfg.xml are actually really used. Try to access them with getProperties() on your org.hibernate.internal.SessionFactoryImpl instance.

回答2:

So far there is no way to do this. but also I couldn't find a way to do this with the new

hibernate.id.new_generator_mappings = true

This one will use the new SequenceStyleGenerator but I couldn't configure this. The parameters used for configuration such as "optimizer" and "increment_size" are not passed to the method that configures the generator.

My point is, I do not know how this "hibernate.id.new_generator_mappings" is supposed to be used to make use of a hilo optimizer and configure properly and my reverse engineering capability proved unreliable.

To use hilo I had to do this @GeneratedValue(strategy = SEQUENCE) which works for testing but it's not a good option for me.

thanks @xwoker but i couldn't get it done.

来源：https://stackoverflow.com/questions/19694154/hibernate-cfg-xml-configuration-for-sequence-generator

标签

hibernate

hibernate-mapping

sequence-generators